Joe Biden's son Hunter is rejecting assertions by President Donald Trump and his Republican allies that he did anything wrong in engaging in foreign work in Ukraine and China.

Pompeo did not say whether he thought the contents of the July 25 call were inappropriate or whether he believed they warranted the complaint of an intelligence community whistleblower at the centre of the impeachment probe.

In the call, Trump raised with the Ukrainian president unsubstantiated allegations that Biden had sought to interfere with a Ukrainian prosecutor’s investigation of his son Hunter.